Means for controlling alternating currents



E. F'. W. ALEXANDERSON. MEANS FOR CONTROLLING ALTEBNATING CURRENTS.

APPLICATION FILED APILZO; |9l8-- 1 ,328,473. Patented Jan. 20,1920.

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APPLICATION FILED APR-20 191B- 1,328,473, Patented Jan. 20, 1920.

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UNITED STATES PATENT OFFICE.

ERNST F. W. ALEXANDIERSON, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MEANS FOR CONTROLLING:- ALTERNATIN CURRENTS.

Specification of l 'ietters Patent.

Patented Jan. 20, 1920.

Application filed April 20, 1918. Serial No. 229,686.

To all whom it may concern:

Be it known that I, ERNST F. V. ALEX- ANDERSON, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have 1nvented certain new and useful Improvements in Means for Controlling A lternating Currents, of which the following is a specification.

My present invention relates to' electromagnetic apparatus for use with high frequency alternating currents either for controlling the fiow of such currents in a circuit, for doubling the frequency thereof or for similar purposes. More particularly my invention relates to electromagnetic apparatus of a kind which I term magnetic amplifiers, such, for example, as are described in my U. S. Patent #1,206,64l3. The.

present application is a continuation in part of my prior application, Serial No. 63,438, filed November 26, 1915.

The object of my invention is to improve the construction of magnetic amplifiers of the class described in the above-mentioned patent in order to render them more efficient for the purpose for which they may be employed. The operation of such devlces is based upon the fact that the energy per cycle of high frequency currents is comparatively small and consequently the energy stored in the electromagnetic field of the generator circuit is comparatively low. As an amplifier of variable currents of comparatively low frequency the device operates by modifying the magnetic field of the high frequency circuit in accordance with variations in the current to be amplified, and inasmuch as the energy necessary to modify this magnetic field is proportional .to the energy stored during eachw cycle it may be shown that it is possibleto construct a magnetic amplifier with a ratio of ampli-j fication equal to the ratio between the frequency .ofthe high frequency current and that of the current which is to be amplified. -When the frequency of the current which is to be amplified approaches zero the theoretically possible ratio of amplification would thus approach infinity. The theoretical foundation for this principle of amplification is, as follows: I

The energy stored in a magnetic field is represented by the quantity Lz' where 'L is the coeflicient of self-induction and dis the magnetizing current. If the current varies in accordance with the sine wave law, the voltage induced at the terminals of the magnetizing winding is QwfLz', where f is the frequency and z is the effective or tie root mean square of the alternating current. The magnetizing current 2' is a wattless current, being 90 .out of phase with the Voltage and thevoltamperes or apparent power required to maintain an alternating current field at any particular frequency is thus Q'rcfLi It can be seen from the two above expressions, for energy stored in the electric field and the apparent power required to maintain this field at any particular frequency that there is a definite numerical re lation between the energy per cycle and the voltamperes needed for magnetization that depends upon the frequency only. Thus we cansay generally that the voltamperes of magnetizationequal 21: times frequency per seqgind times energy stored in the magnetic fie When my device is employed as an amplifier it is used as a high frequency impedance in order to control the flow of power from an alternator with constant field excitation, or an equivalent source of high frequency power. The flow of power can be controlled by either inserting the impedance in series with the load or in shunt with the source of power, or by some combination of these methods. In either case the maximum voltamperes which must be absorbed by the impedance is of substantially the same order of magnitude as the power flowingin the load circuit.

In the case of an inductive impedance like the-device described the energystorcd and released in the magnetic field during each half-cycle is of the same order of magni tude as the power flow in the main circuit. The method of controlling the inductive impedance is to super-impose another flux in thesamc magnetic structure. The controlling fiux saturates the iron and thereby limits the pulsations of the high frequency flux. The controlling flux must, therefore, be of the same order of magnitude as the high frequency flux and the energy stored in the magnetic field of the controlling flux is, therefore, of the same order as the high frequency flux. If the controlling flux is constant no energy flow is needed in the controlling circuit and, the rate of amplification nite frequency or combination of several frequencies, there must be an energy flow in the magnetizing winding of the control flux in order to change the amount of energy stored in the same flux. This fiow of energy is substantially wattless inasmuch as the energy during the first part of each halfcycle is returned during the second part of the same half-cycle. However, the current necessary for this transfer of energy is ofa character of an ordinary w attless magnetizing current. It may be seen from the preceding that the voltamperes consumed by this controlling magnetizing current must transferduring each cycle of its pulsations an amount of energy corresponding to the change in energy stored in the controlling field and consequently the voltamperes needed for magnetization of the control winding are as much lower than the high frequency power that is being controlled-as the frequency of the control pulsations is lower than the radio frequency. The ratio of amplification is, therefore, the same as the ratio of these two frequencies.

Electromagnetic devices of the present class may be developed in a variety of forms, taking lnto account the principles, as above explained. The preferred form is that in which the structure consists of a magnetic circuit with a high frequency winding interlinked therewith and a controlling winding so related to the high frequency winding that there will be substantially no flow of high frequency current in the controlling winding. This may be accomplished either by making the controlling winding inductively independent of the flux induced by the high frequency winding, or by so ar-- ranging the windings that the controlling winding has one portion interlinked with the high frequency flux in one direction and another equal portion interlinked with the high frequency flux in the opposite-direction so that the induced potentials are neutralized in the winding itself.

The features of my invention which I consider novel are pointed out with particularity in the appended claims; The invention itself, however, together with further objects and advantages will best be understood by reference to the following description .taken in connectionwith the accompanying drawings in which Figure 1 shows one-modification of my inventionfFi'g. 2 is an elevation of a structure in which the magnetic circuits and windings are shown in Fig. 1; Fig. 3.is a vertical section taken on line 3-3 of Fig. 2; Figs. 4 and 5 show modified forms of elements which may be used for' building up the devices shown in Figs. 2 and 3 and Figs. 6 and 7 show systems in which my invention may be utilized.

rent losses.

In the form of my invention shown in Fig. 1 two magnetic cores .1 are provided with windings 2 for carrying the high frequency. current. ,The windings are so arranged that the fiux is in opposite directions in the two cores and as a result the high frequency flux fiows'only through the cores 1 and through small portions 3 of the structure adjacent the cores. A second winding 4 which is adapted to carry the controlling current is wound around both ofthe cores as indicated: The flux produced by this winding traverses the two cores in the in each turn. It will also be noted that the controlling winding covers substantially the entire length of the high frequency magnetic circuit.

In the operation of my invention, if the control flux is greatenough to saturate or almost saturate the high frequency core, the permeability of the magnetic circuits is changed and the impedance of the high frequency circuit is modified accordingly. The object of the present design of amplifier is to get as effective control of the high frequency current as possible by producing a Variation of impedance over a wide range in the high frequency winding. In any transformer structure there is a certain amount of leakage in the air surrounding the winding which creates a leakage reactance in addition to the reactance of the flux in the iron core.' This leakage reactance in air cannot be controlled because the permeability of air is constant. Hence the greater the leakage reactance, the less eflicient the control. Also, since the voltamperes required to produce this leakage flux is of no effect in controlling the high frequency current the degree of amplification is reduced because of this leakage. In the present case I have reduced the leakage reactance to a minimum by bringing the two windings as close together as possible and making the controlling-winding cover substantially the entire length of the high frequency magnetic circuit. 7

In Figs. 2 and 3, Ihave illustrated a ractical construction for a device embo ying the form of my invention illustrated in Fig. 1. In constructing electromagnetic devices of the class under consideration it is customary to build up the cores with thin sheets of magnetic material, separated by insulating layers to avoid excessive eddy cur- When iron, such as is usually employed for ordinary frequencies is used with high frequency current, the skin effect respondingly greater amount of iron. The controlling current flux which is needed to saturate the iron will also be correspondingly greater. The degree of amplification depends upon the ratio between the high frequency energy controlled and .the energy necessary to produce the saturating flux. If the saturating flux is greater on account of'such skin effect, the amplification is therefore correspondingly smaller.

In order to' overcome this skin effect and I obtain an increased efficiency in the amplifier, I may use an iron scale which is obtained in the annealing ofsilicon steel. This scale is about one and one-half mils in thickness and has high resistance. These characteristics tend toward reducing the skin effect, in fact, it has been found by careful tests that skin effect is entirely absent at ordinary radio frequencies. I have found also that sheets of other magnetic material, such as electrolytic iron or silicon steel, may be made thin enough so that they have no appreciable skin effect at radio frequencies.

The losses in a device of this nature which appear in the form of heat are considerable, and therefore it is desirable that the magnetic core should be well cooled. In building up a core of thin flexible sheets, such as those which I preferto use, however, it is difficult to provide ventilating spaces between laminations in the usual way. .To'

' overcome this difliculty I first build up elements for the core structure by fastening together, by means of an adhesive, alternate sheet'of iron and paper, or other insulating material of the desired shape and size, until a rigid body is formed and one I which is not too thick to radiate the heat easily from the inner layers. In practice I find that about one-sixteenth of an inch is a suitable thickness for these elements. As

'shownin Figs. 2 and 3, the elements 19 which form the high frequency magnetic circuit have the shape of a hollow rectangle with thev high frequency'windings 20 and 21 around the two sides of the rectangle. In building up the core these elements 19 are interleaved with the short rectangular elements 22 at their ends, and these elements in turn are interleaved with the elements 23' which form the sides of the magnetic circuit for the controlling flux.- The elements 24 and 25 which form the top and bottom of the magnetic circuit are also interleaved between the side elements. With this arrangement it will be seen that spaces are provided for ventilation or for the circulation of a cooling fluid between all of the elements making up the complete structure.

The controlling winding is also made up of a plurality of coils 26 withspaces between.-

The magnetic structure, with the coils thereon, is held firmly in place between the frame members 27 and 28 by means of bolts 29.

Since the high frequency flux is confined almost entirely to the elements 19' and the other elements carry only the controlling flux of comparatively low frequency, it is pling 35. In this case the controlling winding is dispensed with and the controlling current is supplied to the windings 33. Current for producing a constant saturation of the magnetic structure at which the device will operate most efliciently is supplied by means of a direct current source 36. The telephone current for controlling and modulating the current in the antenna is furnished by means of the local circuit of a telephone transmitter 37 which is supplied with current from the battery 38. The current in this local circuit is supplied to the windings 33 through the transformer 39.

The amplifying effect may/ be increased by 1nserting an adjustable condenser 40 in series with high frequency windings in order that-the impedance of the shunt circuit may.

bereducedto a minimum when the current s at a m'axlmum. Condensers-4:1 and 42 are lnserted in the circuit and the value of these condensers is so chosen that they offer comparatively low impedance to the low frequency current flowing through windings 33 but a high impedance to the telephone current. supplied from the secondary of transformer 39. It will be observed that the high frequency currents flow through the two windings in parallel while the telephone current and the constant direct current from source 36 flow through the windings in series. The points 43 and 44 at which the controlling-currents are supplied to the windings are at equal, potentials with respect to the high frequency current, and therefore there is no .tendency for high frequency current to flow through the circuits which supply the controlling current.

In Fig. 7 I have shown another modification which may be employed in carrying my invention into effect. In this case the high frequency alternator45 is connected in series with the antenna 46 and two high frequency windings in shunt to the generator surround the rings 47 and 48. These rings are prefbattery 50 sends a controlling current. through the two windings in series. Withthis arrangement, as well as with the one shown in Fig. 6, it will be evident that the flux produced by the high frequency ourrent is linked as closely as possible with the fiux'produced by the controlling current and that the -high forces in the controlling circuit being equal and opposite to each other no high fre-,

quency currents will flow through the battery 50 when key49 is closed. Condensers 51 inserted in the high frequency circuits prevent the short circuiting of the battery 50, and variable condensers 52 maybe used to increase the amplifying effect, as in the arrangement shown in Fig. 6.

WVh1le 1n the above descrlptlon I have illustrated and expla ned two systems whereby my invention may be carried into effect it will be apparent that many modifications in the structure of the apparatus used and in the application thereof may be made without departing from the scope of the appended claims.

"What I claim as new and desire to secure by Letters Patent of the United States, is.

1. Means for controlling the flow of high frequency currents comprlsing two magneticcores and a winding on each core, means for causing the high frequency current to be controlled to flow through the two windings in parallel and means forcausing a controlling current to flow through the two windings in series.

2: Means for controllingthe flow of high frequency currents comprismg two magnetic cores and a winding oneachcore, means for causing the high frequency current to be controlled to flow through the two windings in parallel, and means for causing a controlling current to flow through the two windings in series, the windings being so arranged with respect to the sources of controlling and higlr frequency current that at .any instant the fluxes produced by the two currents in one of the cores are in the same direction, and in the other core are in opposite directions. 3. Means for controlling the flow of high frequency electro-motive frequency current, a circuit supplied by said source, two magnetic cores having windings thereon which are included in parallel in thehigh frequency circuit, and means whereby the variable electric current is caused to flow through the windings in series.

Means for amplifying a variable electric current comprising a source of high frequency current, a circuit supplied by said source, two magnetic cores having windings thereon which are included in parallel in the high frequency circuit, and means whereby the variable electric current is caused to flow through the windings in series so that at any instant the fluxes produced by the currents in one of the cores are in the same direction and in the other core are in opposite directions.

6. Means for amplifying a variable electric current' comprising a sourcev of high frequency current, a circuit supplied by said source, two magnetic cores having windings thereon which are included in parallel in the high frequency circuit, andmeans whereby the variable electric current is caused to flow through the windings in series and thereby vary the an'lplitude of the high frequenc-y current in accordance with the variations in said variable current. r

7. Means for controll ng the flow of high frequency current con'lprislng two magnetlc cores, a winding on each core, means for causlng the hlgh frequency current to be controlled to flow through the two windings in parallel, and a source of controlling current connected to said windings in such away that the controlling current will flow through the wlndlngs in series, and said source will be unaffected by high frequency 

